Khundra, chair parts are about the most difficult parts to make. The equipment to make a chair bottom is very expensive and grnerally NOT available for rent. If you have to have a full wood bottom, you will be much further ahead to buy new chairs.
You might want to look at woven cane as an alternative. Since this is hand work, it gets expensive to have done and that's even if your present chair design allows it. I suggest that you check books at your library to see what processes and materials are available and what is required to do caning.